Various commercial consumer goods are increasingly using glossy holographic style imaging. These image effects are appearing on product packaging such as, for example, toothpaste and magazine covers.
The holographic style image is created by light reflecting from an object, the outer layers of which include an outermost diffraction pattern-embossed coating, a metalization layer, an adhesive layer and a substrate layer. The diffraction pattern coupled with the reflective property of the metal creates the holographic effect. The adhesive layer bonds the metalized surface of the embossed coating to the substrate. Typically the substrate is a paper or paper-like composition.
Generally, the multilayer composite is created in several steps utilizing coating transfer. A conventional process involves application of a release layer onto a carrier film. Then an embossing material layer is placed on the release layer. The diffraction pattern is next created by embossing the carrier/release/coating composite. Next, the exposed and embossed surface of the coating layer is metalized, i.e., a thin layer of reflective metal is deposited thereon. The substrate is prepared by applying to its outer surface a layer of suitable adhesive. The metalized surface of the carrier film composite is joined to the adhesive-bearing substrate after which the adhesive is activated to form a permanent bond. Lastly, the carrier film is pulled away from the substrate. Separation of the release layer from the coating layer transfers the embossed metalized coating layers adhered to the substrate. The substrate is then incorporated into selected end use applications.
Common traditional processes suffer from the need to employ a release layer between the carrier and the embossing material layer. The release layer composition provides compatibility between the carrier material and the coating material such that they can be carried through the embossing and metalizing steps while remaining intact. The release layer also must have a properly weak bond to the coating layer such that after activating the permanent adhesive layer, the carrier with release layer can cleanly strip away from the finished substrate. Use of release layer adds to the cost of the materials, cost of equipment to apply the materials and complexity of the process for making the product. In short, use of a release layer is undesirable as it reduces productivity and increases cost to of the holographic style image-bearing substrate product.
Another conventional holographic image transfer technique includes coating a carrier film, such as polyester, with an embossable material, embossing and metalizing the composite. The film metalized embossed composite is laminated to a substrate product and the carrier film is not removed, that is the image is viewed through the carrier film layer remaining on the product. It is desirable to have an image transfer film technology in which the carrier layer can be removed, recovered and, to even better advantage, recycled.
It is desirable to have a simpler, more easily utilized, less wasteful and lower cost method to transfer embossable metalized coating layers to suitable substrates that does not employ a release layer.
U.S. Pat. No. 4,473,422 teaches a method for producing a metalized paper or board product having a bright surface and improved scratch resistance, comprising a transfer metalization technique utilizing a tie coat applied to the metal layer and a pressure-sensitive, adhesive coat applied to the tie coat, the adhesive coat binding the metalized composite to the paper or board base. The adhesive coat is applied to the paper or board base in the dry state and in combination with the adjacent tie coat, forms a hard, stable bond with the base that favorably withstands subsequent deformation of the paper or board product. A top coat utilizing a particular solvent mixture, offers consistent wettability of adhesive release coats, and provides a smooth, continuous outer surface for the final product. U.S. Pat. No. '422 differs from the present invention in several ways. The present invention applies a coating to a base polyester film, which is then embossed and metalized. The present base film is releasable after the embossing process has taken place.
U.S. Pat. No. 7,157,135 describes embossable films and methods for making embossable films for creating holograms and diffraction gratings. The embossable films include a base substrate film and a co-extruded embossable layer. The embossable layer is coated with a transparent high refractive index (HRI) coating. The patented invention does not offer transfer release.
Transfer techniques to apply metallic coatings to substrates, such as fabric, leather or plastic surfaces, have been in use for a long time. Thus, the technique of gold leaf transfer was utilized in the 19th century by bookbinders, who employed gold foil transfer sheets to attach gold letters to leather bindings. The transfer sheets comprised a waxed carrier web over which a sheet of gold foil was placed, the gold foil coated on its free side with a heat-activated adhesive layer. In practice, the transfer sheet was hot pressed with a heated die to adhere the metal foil to the leather, and the carrier was thereafter stripped away. The waxy parting layer that was coated initially over the carrier, served to maintain the gold leaf in position on the carrier prior to its transfer, and to permit release of the carrier after the gold had been affixed to the leather.
In recent times, the advent of vapor deposition of metals, such as aluminum and the like, has spurred further interest in the use of this metalization technique for the preparation of a variety of metalized substrates. Thus, techniques of both direct and transfer coating have been attempted on a variety of base materials. There is a need for a method to provide a metalized embossed composite material into a substrate without requiring a release layer between the composite material and a barrier layer.